Photographic film



' Sept- 10, 1940. R. sQPoTTER ET AL 2,214,205

PHOTOGRAPHIC FLM Filed June 8, 1939 INVENTORS Enz/M15.' vlucifer -`Patented Sept. 10, '1940 UNITED STATES [PATENT oFF-ica PHOTOGRAPHIC FHM Application June 8, 1939, Serial No. 278,108

s claims.

parent protective coating for the emulsion or.

light-sensitive layer of such a lm, so as to avoid abrasion of the lm before development, while not interfering with retouching or etching of the film when necessary, or in any way affecting printing or sacrificing clearness.

It is old to protect a film by coating with a layer of clear gelatin, but this has the objection that after the lm is developed, the outer surface of the gelatin coatingis smooth and glossy and makes it difficult to retouch the film, and if the protective coating contains a matting ingredient, this shows as graininess in the printing or results in loss of ne definition of the subject.

An object of the invention -is to provide a film with a protective coating which after developing has a rough, non-glossy surface that can easily be retouchedor etched.

Another purpose of the invention is-to prevent abrasion marks on the film by applying to it a protective coating made up of materials such that when the film is developed and placed in water or processing solutions, certain soluble portions in the coating will be removed while certain non-soluble portions will remain, leaving a hardened coating with a non-glossy, rough surface that is minutely broken or sponge-like in characterl the remaining hardened coating being of such character that the surface can readily lbe retouched or etched.

More particularly the invention has for its objective to aord a protective coating including two or more water-soluble materials and a hardening agent which acts upon one of the watersoluble materials to render it insoluble'in water, while the other soluble material is not affected by the hardening agent and is removed-during processing of the film.

To these and other ends, the invention consists in the construction that will appear clearly from the following description when read in conjunction with the accompanying drawing, the novel features being uointed out in the claims following the specification.

The drawing shows the invention applied to a conventional photographic film.

Referring to the drawing, l deslgnatesa lm base or support, 2 is a photographic or lightsensitive layer or emulsion, and 3 is a protective coating applied. over the. light-sensitive emulsion layer 2, and composed of the materials that will v now be described.

The coating 3 is clear, transparent, and ilexible, and preferably formed of a mixture of two or more water-soluble materials combined with a hardening agent such as chrome alum or potash alum, that acts only onone of the water-soluble 5 materials. As a consequence. the other water-- soluble material is removed during processing or washing of the lm, leaving the non-soluble material and hardening' agent over the surface of the film as a permanent coating of rough and 10 sponge-like or porous characterthat will take a retouchng pencil or can be etched easily.

Water-soluble materials that are not affected by the hardening agent and can be successfully used are poly-ethylene glycol, methyl cellulose, lli sorbitol phthalate, or mannitol. phthalate, while the soluble materials that are hardened and remain on the lm as a permanent coating are water-soluble gums such as gum arabic, karaya, or tragacanth, gum arabic being especially adapt- 20 'ed to the purpose since the hardened gum retains its structure on drying to a maximum de- Y gree.` J

The proportions of the several materials, or their equivalents, used in the coating material 25 may be varied to suit diierent conditions. As an example of one practical embodiment, the coating may consistof 2.5 parts of gum arabic, 2.5A parts of poly-ethylene glycol, 1 part chrome alum, and parts parts water, the coatingE be- 30 ing applied to the surface of the film in a conventional manner as well known in the art, and permitted to dry thereon.

During processing of the film, the poly-ethylene glycol, or other water-soluble material that is not 35 aected by the hardening agent, is dissolved and removed from the coating, leaving the gum arabic or other than non-soluble material in a permanently hardened condition of porous or sponge-like formation on the surface of the film. 40

While the invention has been described with reference to the particular details herein disclosed, it is not confined to the materials set forth, and this application is intended to cover y any departures or adaptations coming within 45 the purposes of the inventionor the scope of th following claims.

We claim:

1. An undeveloped photographic lm including a support, a light-sensitive layer on the sup- 50 port, and a protective coating over the lightsensitive layer, said protective coating comprising substantially 2.5 parts gum arabic, 2.5 parts polyethylene glycol, and 1 part chrome alum.

2. An undeveloped photographic film including 55 the light-sensitive layer, said protective coating comprising a water lsoluble material and an insoluble material which includes a hardening agent and retains a spongelike structure on drying, said soluble material being unaffected by the 5 hardening agent.

ROWLAND S. POTTER. LAWRENCE WEBSTER. 

